Data Loggers / CR21
This product is no longer available and has been replaced by: CR3000. Some accessories, replacement parts, or services may still be available.
CR21 Micrologger®
Services Available
Repair No
Calibration No
Free Support No


The CR21 and CR21L were initially replaced with the 21X and 21XL. Although these data loggers have been retired for many years, replacement parts remain available.

Note: The CR21 and CR21L were identical except that the CR21 was powered by alkaline batteries and the CR21L was powered by rechargeable batteries. Within this document, CR21 refers to both models except where specifically stated.

The CR21 featured an integrated design with built-in power supply, keyboard, and display. It looks very similar to, and is often confused with its replacement, the 21X Micrologger. The CR21 stored up to 608 data points in internal memory.

A typical field-based CR21 consisted of the following:

  • CR21 or CR21L Micrologger with CR21 Instruction Set (PROMs)
  • Alkaline or Rechargeable Power Supply (in base)
  • Weatherproof Enclosure (new and old)



Single-Ended Analog Inputs 7 (-0.2 to +2.5 Vdc or -2 mV to +25 mV, FSR)
Pulse Count Channels 2 (150 Hz [CH 8] and 50 Hz [CH 9], maximum input frequency)
4 Vac Excitation Channels 1
2 Vdc Sensor Excitation Channels 3
Binary Inputs 2
Control Outputs 4
5 Vdc Power Terminals 1
12 Vdc Power Terminals 1
Serial I/O Port 1

FAQs for

Number of FAQs related to CR21: 1

  1. A practical maximum is to connect one multiplexer per every two control terminals on the data logger. Control terminals can be shared between multiplexers to increase the number of connected multiplexers. Sharing terminals, however, requires more complex wiring and programming. Users who would like to connect more than one multiplexer per every two control terminals are advised to contact a sales or support engineer at Campbell Scientific for assistance.